The present invention generally relates to an article wrapping device, and, more particularly, to an end sealing apparatus and method for an article wrapping device.
Horizontal wrapping machines of various types are well known in the material handling art and typically comprise a forming box structure through which an elongated sheet of flexible wrapping material is drawn. The forming box is operative to continuously form from the sheet a forwardly moving tube having a rearwardly disposed open inlet end, and a laterally projecting "fin" defined by drawn-together side edge portions of the sheet. An article in-feed system is used to insert articles to be wrapped into the open tube inlet end. The inserted articles, in a longitudinally spaced array, are then carried within the wrapping material to as it forwardly exits the forming box. The individual articles, or associated groups of articles, as may be the case, forwardly transported within the tube are spaced apart by spaced longitudinal sections of the tube.
As the article-containing tube exits the forming box, the fin portion of the tube is drawn between, and heat sealed by, an opposed pair of counter rotating heat sealing jaws. The sealed fin is then passed through a foldover station, which operates to fold the sealed fin over onto an adjacent portion of the tube. The tube, with its sealed and folded over fin, is then passed through a cutting and sealing station which operates to compress, heat seal, and transversely cut the longitudinal tube sections between longitudinally adjacent article pairs, or sets, to form individual, article-containing packages with sealed opposite ends.
In conventional wrapping machines, this final sealing and cutting process is typically performed by passing the tube through a pair of opposed, counter-rotating cutting and sealing bar structures, or jaws, which intermittently mesh at radially outer ends thereof to simultaneously compress, heat seal, and cut each longitudinal cut tube section as it passes through the cutting and sealing station. To effect this process, one of the jaws is provided with a cutting knife interposed between first and second corrugated heat sealing sections, while the other jaw is provided with an anvil portion interposed between first and second corrugated heat sealing sections which are mere mirror images of the corresponding corrugations on the knife-carrying jaw.
As a given longitudinal tube section passes between the rotating jaws, the outer jaw ends cooperate to sequentially mesh their first corrugated sections to form a corrugated heat seal along a lead portion of the tube section, force the cutting knife through the tube section and against the anvil to cut away the heat sealed tube section from the balance of the tube section, and then mesh the second corrugated sections of the jaws to form a corrugated heat seal along the balance of the longitudinal tube section.
The speed of the tube section, and subsequent rate of end sealed individual packages produced by the horizontal wrapping machine is dependent upon the rate at which the counter-rotating jaws can seal and separate the ends of the longitudinal tube. The rate at which the counter-rotating jaws can seal and separate the end seals of the tube section is determined by the thermal properties of the flexible wrapping material, the temperature of the counter-rotating jaws, and the time of contact of the counter-rotating jaws with the area of the longitudinal tube which is to be sealed and separated.
For many packaged articles, the rate of the horizontal wrapping machine is increased by using a flexible wrapping material with thermal properties facilitating a rapid end seal with a minimum temperature and time application. However, it is often necessary to package items in materials which do not facilitate a rapid sealing time or lower temperature application. For example, when forming Modified Atmosphere Packaging (MAP), the items to be packaged are sealed in packages having a special gas, or gases, therein. The materials to form MAP, however, typically have thermal properties which inhibit the same speeds of sealing time and temperature as the thinner materials used for articles which do not require MAP. Therefore, it is not always possible to increase the rate of the horizontal wrapping machine by using a flexible wrapping material which facilitates forming end seals with a minimum time and temperature application.
Another method of increasing the rate at which the end seals can be created in the longitudinal tube, is to increase the temperature of the counter-rotating jaws. However, there is a maximum temperature at which the wrapping material of the longitudinal tube will be adversely affected. Therefore, there is a limitation in the ability to increase temperature of the counter-rotating jaws to increase the rate of the end sealing device in a horizontal wrapping machine.
Because the prior art end sealing devices use counter-rotating jaws which rotate in a fixed location, using materials which have slower bonding thermal properties, such as for MAP, traditionally has decreased the rate at which the counter-rotating jaws can seal and cut the longitudinal tube. To overcome this difficulty, some prior art devices have used a step and repeat mechanism. In a step and repeat mechanism, the sealing and cutting jaws are forced into engagement with the longitudinal tube, and are moved to follow the linear progress of the longitudinal tube. However, the step and repeat mechanisms of the prior art require complex pneumatic or hydraulic devices and tracks for engaging and disengaging the longitudinal tube, and for following the longitudinal tube while the cutting and sealing jaws are engagement therewith.
In view of the foregoing, it can be seen that a need exists for an improved apparatus, and associated methods, for producing end seals on individual flexible packages discharged from horizontal wrapping machines, and the like, at an increased rate. It is accordingly an object of the present invention to provide such an improved apparatus and methods thereof.